This invention relates to the treatment of skin conditions such as inflammatory skin diseases and various kinds of skin tumors by the topical administration of medicaments. In accordance with this invention, it has been discovered that certain dicarboxylic acids and derivatives of these acids are capable of carrying therapeutically active agents into diseased cells where these agents can control, inhibit or eliminate the abnormal cell processes responsible for the disease condition. These dicarboxylic acids and acid analogs not only enhance the degree to which the therapeutic agents penetrate the cells to reach the regions of interest, but also suppress the overall toxicity of the agents, decreasing or eliminating the damage which they would otherwise do to the living organism and its normal cells. The dicarboxylic acids and acid analogs enhance penetration of medications across the cell wall and stratum corneum, reduce the occurrence of cell and skin injury by the medications, and potentiate the therapeutic activity of the agents. The acids and analogs are thus useful as carriers of the therapeutic agents which are otherwise poorly penetrating or which otherwise have undesirable toxic side-effects en route to sites where the agents can have a valuable therapeutic effect. Included among the derivatives of the acids are mono- and dimercapto derivatives, salts, esters, amides and anhydrides. Still further penetrating ability can be achieved by combining the acids and acid derivatives with stratum corneum penetrants in a topical application.